A number of motionless mixer types exist, such as Multiflux, helical and others. These mixer types, for the most part, implement the same general principle to mix fluids together. In these mixers, fluids are mixed together by dividing and recombining the fluids in an overlapping manner. This action is achieved by forcing the fluid over a series of baffles of alternating twisted geometry. Such division and recombination causes the layers of the fluids being mixed to thin and eventually diffuse past one another. This mixing process has proven to be very effective, especially with high viscosity fluids. These mixers are typically constructed of a series of alternating baffles, of varying geometries, usually consisting of right-hand and left-hand elements disposed in a conduit to perform the continuous division and recombination. Such mixer types, while effective in mixing together most of the fluid being mixed, have a tendency to leave streaks of unmixed material in the extruded mixture. These streaks result from channels of fluid forming along the interior surfaces of the conduit that pass through the mixer essentially unmixed.
It has been found that motionless mixers utilizing baffles that have greater degrees of twist are more effective at reducing this streaking phenomenon (e.g., a mixer using 180xc2x0 baffles will have less streaking than a mixer that employs only 90xc2x0 baffles). Using baffles with greater degrees of twist, however, raises its own issues. As the degree of baffle twist increases, the length of the mixer required to maintain flow rates equivalent to mixers with baffles of lesser twist also increases. Such an increase in mixer length is unacceptable in most motionless mixer applications. Users of motionless mixers, typically, need to be close to the work piece they are applying the mixture to. The longer a mixer becomes the less manageable it is to work with. In addition, longer mixers will generally have a higher retained volume, entrapping more fluid when the mixer is disposed.
There have been attempts made to maintain adequate mixer length while trying to remedy the streaking problem. Much of this effort has focused on using a combination of mixing baffles of varying degrees of twist (e.g., mixing 90xc2x0 elements with 180xc2x0 or 270xc2x0 elements). In such designs, the bulk of the mixing is done in the baffles of lesser twist (i.e., the 90xc2x0 elements), which reduces the overall length of the mixer, and then, in the baffles of greater twist (i.e., 180xc2x0 or 270xc2x0 elements), the fluid moving along the outer periphery of the mixing elements (i.e., along the interior surface of the conduit) is forced into the center of the mixing elements, but only temporarily. In these arrangements, such fluid is eventually worked back to the outer periphery. Examples of such approaches are described in U.S. Pat. No. 3,239,197 to Tollar and U.S. Pat. No. 5,851,067 to Fleischli et al. While such approaches tend to reduce the width of the streak, the streak is not eliminated. Accordingly, there is a need for a motionless mixer that more effectively reduces streaking while maintaining acceptable mixer length and flow rate. There is also a need to do this in a cost effective manner.
According to one aspect of the present invention, a motionless mixer includes a conduit and a flow inversion baffle disposed in the conduit in which the flow inversion baffle has a center to perimeter flow portion, a perimeter to center flow portion and a perimeter flow diverter. Fluids introduced into and flowing within the conduit are mixed together by moving the fluids flowing in the center of the fluid flow to the perimeter of flow and by also moving the fluids from the perimeter of the fluid flow to the center of flow. The mixer may also have a plurality of baffle elements. At least one baffle element may be a right-handed baffle element and at least one other baffle element may be a left-handed baffle element. The baffle elements may be integral with one another, and a sidewall may be formed integral with the baffle elements. The baffle elements may be formed by injection molding.
According to another aspect of the present invention, a motionless mixer includes a conduit, at least one flow inversion baffle disposed in the conduit and a plurality of alternating mixing baffles disposed in the conduit. The flow inversion baffle has a center to perimeter flow portion, a perimeter to center flow portion and a perimeter flow diverter. In this aspect of the invention, the center to perimeter flow portion has a chamber wall that defines a center to perimeter flow chamber having an entry and an exit, and the perimeter to center flow portion has a chamber wall that defines a perimeter to center flow chamber having an entry and an exit. The center to perimeter flow portion, the perimeter to center flow portion and the perimeter flow diverter may be integral with one another. The perimeter flow diverter may surround the center to perimeter flow portion and define the entry to the perimeter to center flow chamber. Further, the chamber wall of the perimeter to center flow portion may define an angled baffle adjacent the flow chamber exit. In one aspect of the invention, the alternating baffle elements are right-handed and left handed baffle elements. The alternating right-handed and left-handed baffle elements may have a 90xc2x0 twist. The conduit of the mixer may be circular, and the flow inversion baffle and the alternating baffle elements may be rounded. The baffle elements may be integral with one another, and a sidewall may be formed integral with the baffle elements. The baffle elements may be formed by injection molding.
According to another aspect of the invention, a method of reducing fluid streaking in a motionless mixer includes providing a conduit having an inlet and an outlet, a flow inversion baffle and a plurality of alternating mixing baffles disposed in the conduit. The flow inversion baffle has a center to perimeter flow portion, a perimeter to center flow portion and a perimeter flow diverter. The method farther includes introducing a plurality of fluids to be mixed to the conduit inlet, forcing the fluids through baffles in the conduit and extruding a mixed fluid composition from the conduit outlet. In another aspect of the invention, a method of making a flow inversion baffle includes providing a set of forming tools that define the structure for a flow inversion baffle having a center to perimeter flow portion, a perimeter to center flow portion and a perimeter flow diverter, setting the forming tools to form a flow inversion baffle mold and injecting plastic resin into the flow inversion baffle mold to form a flow inversion baffle. According to another aspect of the invention, a method of making a baffle assembly includes providing a set of forming tools that define the structure for a flow inversion baffle having a center to perimeter flow portion, a perimeter to center flow portion and a perimeter flow diverter and that further defines a plurality of alternating mixing baffles, setting the forming tools to form a mold for a baffle assembly having a flow inversion baffle and plurality of alternating mixing baffles and injecting plastic resin into the baffle assembly mold to form a baffle assembly.